Modal analysis and testing

Modal Analysis is the study the dynamic response of machines or structures, i.e. the way they vibrate and their frequencies, when excited by a vibrating force or impact.

ISVR Consulting has all the tools necessary for detailed modal analysis of most structures.  In recent times a wide variety of structures has been successfully tested, ranging from a 6 metre steel beam with additions weighing 13 tons, to a small plastic disk of a few millimetres diameter, which is part of a Bluetooth headset.  Modal analysis of existing structural components and prototypes allows potential problems to be seen, with slow-motion video animation of selected modes.

Photo: Measuring the transfer function between an instrumented hammer

Measuring the transfer function between an instrumented hammer
and an accelerometer

A complete set of transfer functions between the force and response of the structure is taken on a grid sufficient to give a realistic visual interpretation of the potential motion of a test piece.  Either an appropriate vibration exciter or the impact from an instrumented hammer may be used to excite the structure.

Measurements are made using a Brüel & Kjær “PULSE” system, with associated instrumentation according to the size and complexity of the test object.  Results of the measurements are analysed using the Modal Analysis software – ISVR Consulting currently use “ME'scope” from Vibrant Technology.

Operational deflection shapes

ISVR Consulting is also able to measure operational deflection modes on a structure which is subject to external forces which cannot be measured. Frequency response functions between a fixed accelerometer and other fixed or roving accelerometers can be animated in the frequency or time domain, thus illustrating, for example, the response of a vehicle driving over a rough surface, or bumps. This would enable visualisation of the suspension behaviour above and below the natural frequency of the suspension, for instance.